Developing and deploying practical grid-level energy storage is a challenge in the area of renewable energy. As renewable and sustainable energy sources, such as wind and solar, are developed, the intermittency factors of these sources become a concern. A need exists for the development of storage systems to level-load or smooth out the peaks and dead times in their power output. In addition to this need, other grid services could be provided by versatile energy storage, including electrical energy time shifting, load following, area regulation, as examples.
Some approaches to grid-level storage include capacitors, flywheels, batteries, compressed air energy storage (CAES), and pumped hydro energy storage. These approaches have several disadvantages, including technical difficulties, high costs, and limited applicability outside of particular niche areas. For example, capacitors are fast-reacting and can sink large currents, but they have limited storage capacity. Their niche area is grid voltage and frequency maintenance through electronic control circuitry. Flywheels and batteries are typically capable of meeting only moderate storage capacity needs. Also, flywheels can be expensive to construct and operate, and batteries tend to have a relatively short lifespan. In the higher capacity range, CAES and pumped hydro energy storage are often preferred; however, site-specific issues dictate where such plants can be placed.
The world's fresh water supplies are being depleted due to a number of different factors. As additional people from various arid and semi-arid regions require water for both irrigation and personal use, aquifers are being depleted at ever increasing rates. Furthermore, climate change is decreasing snowpacks and reducing the size of glaciers such that fresh water derived from these traditionally renewable sources are falling short of their historic levels. Sustainable use of fresh water does not appear to be a priority in developed countries where supplies are being utilized to satisfy an increasing number of uses such as hydroelectric power generation, agriculture, and for use by urban areas for personal and industrial use. It has been estimated that within the next 25 years, water may be shipped in oil tanker-like vessels from areas where it remains plentiful (e.g. Alaska) to regions of the world that suffer from lack of water. If these trends continue, wide spread drought could lead to starvation and conflict. Expensive, energy intensive technology already exists for creating fresh water from non-potable sources. Technologies such as reverse osmosis (RO) and flash evaporation are used where energy sources in the form of electricity and/or heat generation (mostly through combustion) are plentiful. However, when measured in terms of energy needed to produce a unit of fresh water, these techniques are not particularly efficient although RO systems are under continual improvement. Therefore, there is a need for methods of energy efficient production of fresh water using energy sources that are present indigenously in the regions where the water is to be used.